The present invention relates to a method for the production of an ophthalmic element for correcting ametropia, which is adapted for correcting the foveal and peripheral vision.
In order to correct a subject's ametropia, a spectacles lens is used, which is placed in front of the eye in a fixed fashion in relation to the face, using a frame for holding the lens. The central zone of the lens then serves mainly to correct the wearer's ametropia when the lafter looks straight in front. The image of an object viewed under these conditions is detected by a central zone of the wearer's retina, called the foveal zone. For this reason, the visual perception that corresponds to the direction of viewing straight in front is called foveal vision, or central vision. A purpose of the ametropia correction produced by the central zone of the spectacles lens therefore consists of bringing the image of an object which is positioned in front of the spectacle wearer back into the plane tangential to the retina in the foveal zone. Such a correction is only approximate for certain viewing conditions, in particular because the exact position of the image varies along the optical axis of the eye as a function of the viewing distance of the object.
The peripheral zone of the lens, located around the central zone of the latter, also participates in the formation of the image on the retina when the observer looks straight in front, without turning the eyes, for parts of the object that are off-axis. The parts of the image corresponding to the off-axis parts of the object are then located outside the foveal zone, in the peripheral zone of the retina. For this reason, the corresponding visual perception is called peripheral vision.
The defect in the position of the image on the retina when the wearer looks straight in front can vary between foveal vision and peripheral vision. This variation depends on the shape of the wearer's eye and the retinal angular offset. It varies, in general, for different wearers. For this reason, a foveal-vision ametropia and a peripheral-vision ametropia for a given angular offset are distinguished for each wearer, with two corresponding ametropia corrections.
Now, it is known that for a myopic wearer, formation of the image behind the retina leads to an elongation of the eye. Such defocusing thus causes an increase in the degree of myopia of the wearer. This effect is produced not only when the image is formed behind the retina in the foveal zone, i.e. in foveal vision, but also when it is formed behind the retina in the peripheral zone of the latter, i.e. in peripheral vision. In order to avoid such a worsening of the ametropia, it has been proposed to adapt the spectacles lens outside its central zone in order to correct the wearer's peripheral vision. The central zone of the lens thus produces the correction of the foveal vision, and the peripheral zone of the lens, located around the central zone, produces the correction of the peripheral vision. Such an adaptation of a corrective ophthalmic lens is disclosed in the document US 2005/0105047.
But, when the lens wearer views an off-axis object by turning the eyes, the direction of his gaze passes through the lens at a point of the peripheral zone. The optical features of the lens at this point are then no longer suitable for forming an image on the retina along the direction of gaze, i.e. along the optical axis of the eye that is turned. Indeed, the ametropia involved under these conditions along the optical axis of the eye is ametropia of foveal vision, but the optical axis of the eye intersects the lens at a point where the vision correction produced corresponds to the peripheral vision. The ametropia correction produced is then not suited to these viewing conditions, and the wearer's visual comfort is reduced.